Light-emitting silicon's day dawns

A NEW way of tweaking slivers of silicon could let researchers create microchips with tiny, built-in lasers. The technique could be used to make on-chip sensors, or computers using light instead of electrons.

Efforts to get silicon to emit light have intensified over the past 10 years, but even the best methods are still woefully lacking, with an efficiency of only 1 per cent. Other semiconductors, such as gallium arsenide, can produce light with more than 30 per cent efficiency.

The commonest way to get light out of semiconductors is to apply a voltage that bumps electrons in the atoms from a low energy level called a "valence band" to a higher energy level called a "conduction band". The electrons then fall back into the valence band, emitting the energy as light. The problem with silicon is that when electrons fall back, most of the energy they release is absorbed ...

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